The Edinburgh Fringe introduced a tap-to-tip system this year, based on iZettle readers in nice-looking Plexiglass stands. The readers are preconfigured to debit £5 from your card on a tap. That's a bit more than your average street show tip of a pound or two, but really good if you're wandering around without any change - you don't have to feel guilty about watching a street show but not being able to pay at the end.